Chondrocyte-seeded collagen matrices implanted in a chondral defect in a canine model

The objective of our study was to evaluate reparative tissues formed in cho ndral defects in an adult canine model implanted with cultured autologous a rticular chondrocytes seeded in type I and LI collagen-GAG matrices. Two de fects were produced in the trochlea grooves of the knees of 21 dogs, with c artilage removed down to the tidemark. This study includes the evaluation o f 36 defects distributed among five treatment groups: Group A, type II coll agen matrix seeded with autologous chondrocytes under a sutured type II col lagen flap; Group B, type I collagen matrices seeded with chondrocytes unde r a sutured fascia flap; Group C, unseeded type I collagen matrix implanted under a sutured fascia flap; Group D, fascia lata flap alone; and Group E, untreated defects. All animals were killed 15 weeks after implantation. Si x other defects were created at the time of death and evaluated immediately after production as 'acute defect controls'. In three additional defects, unseeded matrices were sutured to the defect and the knee closed and reopen ed after 30 min to determine if early displacement of the graft was occurri ng; these defects served as 'acute implant controls'. The areal percentages of four tissue types in the chondral zone of the original defect were dete rmined histomorphometrically: fibrous tissue (FT); hyaline cartilage (HC); transitional tissue (TT, including fibrocartilage); and articular cartilage (AC). New tissue formed in the remodeling subchondral bone underlying cert ain defects was also assessed. Bonding of the repair tissue to the subchond ral plate and adjacent cartilage, and degradation of the adjacent tissues w ere evaluated. There were no significant differences in the tissues filling the original d efect area of the sites treated with chondrocyte-seeded type I and type II matrices. Most of the tissue in the area of the original defect in all of t he groups was FT and TT. The areal percentage of HC plus AC was highest in group E, with little such tissue in the cell-seeded groups, and none in gro ups C and D. The greatest total amount of reparative tissue, however, was f ound in the cell-seeded type II matrix group. Moreover, examination of the reparative tissue formed in the subchondral region of defects treated with the chondrocyte-seeded collagen matrices (Groups A and B) demonstrated that the majority of the tissue was positive for type II collagen and stained w ith safranin O. These results indicate an influence of the exogenous chondr ocytes on the process of chondrogenesis in this site. In all groups with im plants (A-D), 30-50% of the FT and TT was bonded to the adjacent cartilage. Little of this tissue (6-22%) was attached to the subchondral plate, which was only about 50% intact. Remarkable suture damage was found in sections from each group in which sutures were used. Harvest sites showed no regener ation of normal articular cartilage, 18 weeks after the biopsy procedure. Future studies need to investigate other matrix characteristics, and the ef fects of cell density and incubation of the seeded sponges prior to implant ation on the regenerative response. (C) 1998 Elsevier Science Ltd. All righ ts reserved.